Make discarding-stdout optional?

First, let me say thanks for this awesome library! I'm working on an LSP backend for my own lil' language and was thrilled to find such a well designed and documented library in Clojure =D

I'm using a socket backend rather than stdin/stdout so that I can easily iterate on the LSP backend using the the usual [clj-reload](https://github.com/tonsky/clj-reload)-type REPL workflow. I was confused as to why my `println` and [telemere](https://github.com/taoensso/telemere)/log calls weren't having any effect from within, e.g.

```clojure
(defmethod lsp4clj.server/receive-notification "exit"
[_ context params]
(println "LSP exit notification received")
nil)
```

Then I read the docs more closely and found this `discarding-stdout` https://github.com/clojure-lsp/lsp4clj/blob/4dd6d62dbbe1aeb906b7f88a9a06bf85d4ce19ba/src/lsp4clj/server.clj#L117-L125

Would you be open to making this optional somehow? Either an explicit option that's threaded through or, if that's too onerous, perhaps a dynamic var that can be rebound? I'm happy to knock out a PR if you have a preferred approach.

No worries if not too, I just figured I'd ask in case y'all think it'd be in scope. Thanks!

Start with src/lsp4clj/server.clj around lines 117-125 and the lsp4clj.server/receive-notification entry point, then trace how the socket backend reaches the stdout-discarding behavior. Done means callers can choose whether stdout is discarded, and the socket workflow can emit println and telemere/log output when discarding is disabled.

Written by the indexing model from the issue text.